As of November 2010, Allegiant operates a fleet of 66 McDonnell-Douglas MD-80 series aircraft. The fleet is a combination of MD-81, MD-82, MD-83, MD-87 and MD-88 variants, which hold between 130 to 150 passengers each.
As this aircraft is no longer being manufactured, since McDonnell-Douglas no longer exists and Boeing, which acquired McDonnell-Douglas in the late 1990s has shut down production, all of these planes are used, with ages ranging from 13 to 25 years.
According to the aviation resource PlaneSpotters.net, which specializes in airline fleet information, Allegiant has four Boeing 757-series aircraft on order, as of November 2010. With a range of over 3,000 nautical miles--as compared to the MD-80's, which tops out at 2,700, according to Boeing--the 757 accommodates a similar quantity of passengers to the MD-80, albeit arranged differently.
While the MD-80 configures passengers to rows of two on the left side of the plane and three on the right, the 757--which is shorter in fuselage length as a result--groups passengers in threes on both sides.
Although operating aircraft which are all older than a decade might not seem like something to brag about, Allegiant's decision to compose its fleet as such was a premeditated one to keep it a budget airline.
According to the CBS Interactive Business Network, Allegiant will only fly 13 of the 18 MD-80s it purchased in early 2010 from Swedish carrier SAS (see Reference 4).
In addition to paying cash for the aircraft, which are cheap as compared to others due to market saturation, Allegiant plans to use the five aircraft not designated for flight as spare parts repositories, further cutting its costs and optimizing efficiency.
